1. Field of the Invention
The present invention relates to exhaust purification apparatus and method for an internal combustion engine, the engine having an exhaust passage in which an exhaust (or exhaust gas) purification catalyst is mounted. The exhaust purification apparatus and method according to the present invention perform a poisoning release control of the exhaust purification catalyst when a predetermined condition is established.
2. Description of the Related Art
A Japanese Patent Application First Publication No. 2001-271685 published on Oct. 5, 2001 exemplifies previously proposed catalyst temperature controlling apparatus and method for a direct cylinder fuel injection internal combustion engine.
In the previously proposed catalyst temperature controlling method and apparatus, while, against a poisoning of sulfur of an NOx trap catalyst, a poisoning release thereagainst is being executed, an air-fuel ratio within a cylinder is set as λ=1 and a split of fuel injection into a suction stroke injection (fuel injection under the suction stroke) and a compression stroke injection (fuel injection under the compression stroke) is carried out to raise an exhaust (or exhaust gas) temperature. Thus, a temperature about the NOx trap catalyst is raised to a high temperature at which the poisoning release of sulfur is enabled. In addition, during an execution of the poisoning release, to suppress a worsening of a fuel consumption, as a demand (or request) on a rise in temperature of the catalyst becomes higher, a strength of an intake air ripple is weakened and the compression stroke fuel injection timing is retarded. In a case where a rate of the fuel injection quantity under the compression stroke to a total fuel injection quantity for four strokes of the engine per cylinder is varied from 20% to 60%, an exhaust gas temperature becomes higher as the rate of fuel injection quantity under the compression stroke becomes larger.